Interpretive Summary: Phytochemicals, such as phenolics, have been reported to have potential health benefits. Comprehensive information regarding phenolics in whole grain rice having different bran colors is lacking. This research determined the concentrations of several phenolics and antioxidant capacities in the solvent-extractable and cell-wall bound fractions of whole grain rices and samples of several other cereal grains for comparison. We determined that red and purple rice, in comparison with other light-colored bran rice and other cereals, had significantly higher total (sum of Free- and Bound-) phenolic (PC) and flavonoid (FC) concentrations and antioxidant capacities. The concentrations of the Bound-PC and FC accounted for approximately half of the total PC and FC in the light-colored bran rice, but were lower than those in purple and red bran rice. These results suggest that dark pigmented whole grain rices compared to light-colored bran rice and other major cereals have relatively high levels of several phenolics, which have been proposed to positively impact human health.

Technical Abstract:
To study the polyphenols in whole grain rice varying in bran color, total phenolics, flavonoids and antioxidant capacities of the solvent-extractable (Free) and cell-wall bound (Bound) fractions and the profiles of procyanidins and anthocyanins were determined. Red and purple bran rices had significantly higher total (sum of Free- and Bound-) phenolic (PC) and flavonoid (FC) concentrations and antioxidant capacities than light-colored bran rice or other cereals due to their higher concentrations of proanthocyanidins and anthocyanins, respectively. The concentrations of the Bound-PC and FC accounted for approximately half of the total PC and FC in the light-colored bran rice, but were lower than those in purple and red bran rice. High correlations were found between the concentrations of total phenolics and the three antioxidant capacity assays except those in the bound fraction when related to iron chelating capacity. Procyanidins in red bran rice was 1.27mg/g and its composition was 6.5, 33.5, 30.6 and 29.4% of 1-3, 4-6, 7-10 mers, and polymer (degree of polymerization higher than10), respectively. Cyanidin-3-glucoside was the predominant anthocyanins and peonidin-3-glucoside was the second highest, and the profiles varied between purple bran cultivars. Whole grain rice differing in bran color contained unique polyphenol subgroups, which have been proposed to positively impact human health.